Top 5 for me would probably be:
1. Water- I like a lot of Water Pokemon, looking at things.
2. Fire- First 'mon I ever had was Fire, and some of my favourite in-game teams have had Fire types as the MVP. sorry Grass, you're the only starter type not being represented here
3. Ground- i always have trouble w/ electric types woo also quagsire is so happy
4. Rock- I wish the Fossil Pokemon weren't so late game in like 50% of the games
5. Ice- look bergmite, lapras and the sneasel line are like the entire reason this is here but they're fantastic reasons ok
Favourite is steel, for its gazillion resistances especially before the XY nerf. They go a long way in storyline play, and mean the type pairs well with just about anything else. Steel moves are a bit meh for attacking but that's what coverage moves are for.